1. Field of the Invention
The present invention relates to a mandrel suitable for use in the production of a rubber hose, more particularly to a mandrel having excellent dimensional stability, durability, heat resistance, and releasability.
2. Description of the Prior Art
Various vulcanized rubber hoses such as water hoses and heater hoses are generally produced by the following steps (I) to (VIII), shown in FIG. 1.
(I) An unvulcanized rubber coated mandrel assembly 10 is formed by melt-coating an unvulcanized rubber compound 12, by using an extruder 13, on a mandrel 11 having the same diameter as that of the desired rubber hose (alternatively, an unvulcanized rubber sheet may be wound on the surface of the mandrel 11 instead of the melt coating);
(II) As an optional step, a knitted fiber sheet 14 is applied on the surface of the rubber compound coated mandrel assembly 10 in a knitting machine 15 for reinforcing the desired vulcanized rubber;
(III) Unvulcanized rubber compound 12', which may be the same as or different from the unvulcanized rubber compound 12, is further coated on the knitted fiber sheet coating 14 by using an extruder 16, if the above-mentioned step (II) is used;
(IV) The unvulcanized rubber coating or sheet 17 on the mandrel obtained in the step (I) or (III) is coated with lead in a conventional lead coating machine 18 for preventing deformation of the outer diameter of the hose (this lead coating may be omitted or replaced with a high-melting point resin coating);
(V) mandrel 19 with the unvulcanized rubber and lead is wound up to obtain an unvulcanized rubber assemble 20;
(VI) The unvulcanized rubber assemble 20 thus obtained is vulcanized by heating at 130.degree. C. to 180.degree. C. with, for example, a pressurized steam 23 in a vulcanization apparatus 21 such as vulcanizer (the unvulcanized rubber assemble may be directly fed to a continuous vulcanizer without winding up in the step (V);
(VII) After the vulcanization, the cover (e.g., lead) is removed from the vulcanized product in a cover releasing step 24; and
(VIII) The mandrel 11 is pulled out from the resultant vulcanized rubber hose product 25 by passing a pressurized gas or fluid 26 between the rubber hose and the mandrel.
The mandrels used as a core in the above-mentioned production steps of the rubber hose must have sufficient flexibility to be readily wound up and have sufficient heat resistance to resist a high temperature during vulcanization. Furthermore, the mandrels must have excellent releasability to allow ready removal from the rubber hose during the release step and to provide a fine finish on the released surface of the rubber hose. Furthermore, the mandrels are required to possess, in addition to the above-mentioned characteristics, dimensional stability sufficient not to cause error in the diameter due to shrinkage or elongation of the mandrel and durability sufficient to be repeatedly used many times.
Heretofore, mandrels are generally manufactured from polyamides such as nylon. However, these conventional mandrels have problems in that the flexibility is not sufficient, shrinkage or elongation is caused after repeated use several times to result in dimension problems, and the durability is not sufficient due to, for example, the decrease in the mechanical strength. For these reasons, conventional mandrels can be used repeatedly only two or three times.